Enhancement of APEX model to assess effectiveness of wetland water quality benefits

Authors: SHARIFI, A.S. - Department Of Energy; LEE, S. - University Of Maryland; McCarty, Gregory; LANG, M.W. - Department Of Fish And Wildlife; JEOGN, J. - Texas A&M Agrilife; Sadeghi, Ali; RABENHORST, M. - University Of Maryland

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2019
Publication Date: 4/23/2019
Citation: Sharifi, A., Lee, S., McCarty, G.W., Lang, M., Jeogn, J., Sadeghi, A.M., Rabenhorst, M. 2019. Enhancement of APEX model to assess effectiveness of wetland water quality benefits. Water. 11(3):606. https://doi.org/10.3390/w11030606.
DOI: https://doi.org/10.3390/w11030606

Interpretive Summary: As a part of the USDA Conservation Effects Assessment Project (CEAP), scientists use the Agricultural Policy Environmental Xtender (APEX) model to estimate field-level impacts of conservation practices on soil nitrogen, phosphorus, and carbon in agricultural landscapes. However, the capacity to simulate conservation practices that include establishment, enhancement, or restoration of wetlands has not been well developed in APEX, partly due to the inherent complexity and dynamic nature of wetland water and nutrient cycles, the past deficit of sufficient field data to quantify these cycles, and the difficulty in determining spatial and temporal presence of wetlands in an agricultural landscape. This study improves the current model capacity to represent wetland water quality benefits by adding a new biochemical module into the APEX model. The performance of this enhanced APEX model was tested against observed flows of sediment and various forms of nutrients (carbon, nitrogen and phosphorus) for a wetland located on the Eastern shore of Maryland. Metrics for model prediction uncertainty were evaluated. Results showed that this enhanced APEX model can represent nutrient cycling within the study wetland. The addition of wetland biogeochemical routines to the APEX model improved our understanding of the mass exchanges for these nutrients within wetlands. Overall, the updated APEX model can provide policymakers and managers with proper means for assessing environmental benefits delivered by wetland conservation.

Technical Abstract: The Agricultural Policy & Environmental eXtender (APEX) model has been widely used to assess changes in agrochemicals in response to conservation and management plans led by US Department of Agriculture (USDA)-Conservation Effects Assessment Project (CEAP). However, the existing APEX model is limited in quantification of wetland water quality benefits. This study improves the current model capacity to represent wetland water quality benefits by adding a new biochemical module into the APEX model. The performance of an enhanced APEX model was tested against observed outgoing five water quality variables (e.g., sediment, organic N, NO3, NH4, and PO4) on a wetland within the Eastern shore of the Maryland. Generalized Likelihood Uncertainty Estimation (GLUE) was implemented to assess model uncertainty. Results showed that the enhanced APEX model was capable of representing N and P cycling within the study wetland. The addition of wetland biogeochemical routines to APEX model improved our understanding of wetlands’ mass exchanges within N and P cycling. Overall, the updated APEX model can provide policymakers and managers with proper means for assessing environmental benefits delivered by wetland conservation.